1. Field of Invention
The present invention relates to a power storage module. More particularly, the present invention relates to a power storage module and a power storage device with a power management function.
2. Description of Related Art
With advances in science and technology, there has been an increase in the demand for high power quality. In order to provide an AC sinusoidal wave with a stable voltage, a stable frequency, no electrical surge, no peak disturbance, and no harmonic wave, a power storage device is utilized to suppress mains voltage fluctuations, frequency shifting, harmonic waves, and unbalanced three-phase voltage. The power storage device also provides emergency protection measures when electricity supply failure is encountered or electrical surge occurs unexpectedly. Moreover, with respect to renewable energy, because most power generated by a renewable energy generating apparatus may change a periodically and unexpectedly, when, for example, solar power, wind power, or tidal power is inputted directly into a power grid, this may seriously affect the operation stability of the power grid, thereby limiting the development and utilization of renewable energy. By setting up a power storage device between the renewable energy generating apparatus and the power grid, the power may be buffered and regulated such that the utilization of renewable energy may be increased.
According to power storage technology, traditional power storage devices with a large capacity may be classified into five types. Reference is made to FIG. 1a. FIG. 1a illustrates a conventional single-stage isolation power storage device 100a. The power storage device 100a includes plural power storage modules 110a, and each of the power storage modules 110a includes a storage cell 111 and a DC/AC converter 112. The storage cell 111 is coupled to the DC side of the DC/AC converter 112. In addition, the AC side of each of the DC/AC converters 112 is coupled to one side of a transformer 120 in parallel to isolate the power storage modules 110a. The other side of the transformer 120 is coupled to an AC bus 130. The power storage device 100a collects the power to the AC bus 130 through the transformer 120. The power storage device 100a connects an AC load 140 independently by the AC bus 130 or connects an AC power grid 150 inline by a switch S.
FIG. 1b illustrates a conventional single-stage non-isolation power storage device 100b. Similar to the power storage device 100a, each of a plurality of power storage modules 110b of the power storage device 100b includes a storage cell 111 and a DC/AC converter 112. Each of the power storage modules 110b is coupled to an AC bus 130 in parallel directly. Reference is made to FIG. 1c. FIG. 1c illustrates a conventional double-stage isolation power storage device 100c. Each of a plurality of power storage modules 110c of the power storage device 100c includes a storage cell 111, a DC/AC converter 112 and a DC/DC converter 113. The storage cell 111 is connected to the DC side of the DC/AC converter 112 through the DC/DC converter 113. Similarly, the AC side of each of the DC/AC converters 112 is coupled to one side of a transformer 120 in parallel. The other side of the transformer 120 is coupled to an AC bus 130. The power storage device 100c collects the power to the AC bus 130 through the voltage transformer 120. The power storage device 100a connects an AC load 140 independently by the AC bus 130 or connects an AC power grid 150 inline by a switch S.
Furthermore, FIG. 1d illustrates a conventional double-stage non-isolation power storage device 100d. Similar to the power storage device 100c, in each of a plurality of power storage modules 110d of the power storage device 100d, a storage cell 111 is connected to the DC side of a DC/AC converter 112 through a DC/DC converter 113. Each of the power storage modules 110d is coupled to an AC bus 130 in parallel directly.
Moreover, there is a power storage technology with a more complicated control method. Reference is made to FIG. 1e. FIG. 1 e illustrates a conventional double-stage serial power storage device 100e. As shown in FIG. 1 e, in the power storage device 100e, each output of a plurality of DC/DC converters 113 is connected to each other in series. Each DC side of a plurality of DC/AC converters 112 is connected to each other in parallel. Each of a plurality of storage cells 111 collects the power to an AC bus 130 through the serially connected DC/DC converters 113 and the parallel-connected DC/AC converters 112, connects an AC load 140 independently through the AC bus 130, or connects an AC power grid 150 inline through a switch S.
All of the power storage devices above utilize the storage cells as storage elements. However, the characteristics of conventional storage cells are, for example, low power density, and long charging time, that is, slow response for dynamic load compensation. To be more precise, if the DC/AC converter is a three-phase converter, when the three-phase load is unbalanced, a ripple current with a low frequency of the DC bus which is coupled to the DC side of the DC/AC converter is large. Moreover, a ripple current with a low frequency is distributed between the storage cell and the capacitor of the DC bus and the amount of the distributed current is dependent upon the output impedance. A ripple current with a low frequency may not only increase the heat loss of the storage cell so that the life of the storage cell is affected, but also may result in a wide undulating voltage of the DC bus such that the quality of the current wave is affected and the stability of the power system is decreased. Furthermore, a deep discharge has a significant impact on the storage cell. Normally, the number of charge/discharge cycles of a storage cell seldom exceeds one thousand. Therefore, the maintenance cost of the power storage device with storage cells is increased.
For the foregoing reasons, there is a need for configuring a power storage module more efficiently so that the efficiency of the power storage device and the stability of the power system may be improved.